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J = <a href="%pathto:imop.vl_imwhiten;">VL_IMWHITEN</a>(I,ALPHA) approximatively whitens the power spectrum
of the natural image I. The algorithm assumes that the modulus of
the spectrum decays as 1/f^ALPHA (f is the frequency).
</p><p>
<a href="%pathto:imop.vl_imwhiten;">VL_IMWHITEN</a>(I) uses ALPHA=1 (a typical value for natural images).
</p><p>
<a href="%pathto:imop.vl_imwhiten;">VL_IMWHITEN</a>(I,ALPHA,CUTOFF) also applies a low-pass filter with
cutoff frequency equal to CUTOFF x FN, where FN is the Nyquist
frequency (half of the sampling frequency).
</p><p>
See also: <a href="%pathto:vl_help;">VL_HELP</a>().
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